In my quest to improve my wine making, I've been studying sugars and learned a few interesting things, so I wrote this summary for myself.Sugars In Wine Making Summary

There are 2 main sugars in grapes, Glucose (Dextrose) and Fructose.Fructose tastes 1.73 times sweeter than Glucose.As grapes ripen, the level of Glucose remains relatively constant, while the level of Fructose increases.At typical normal ripening, the levels of Glucose and Fructose in grapes are about equal.Sucrose (table sugar) is a di-saccharide, consisting of equal parts Glucose and Frustose.Late harvest wines will have higher proportion of Fructose.Yeast will only ferment Sucrose after breaking it down, with invertase and acid, into Glucose and Fructose.Yeast will ferment Glucose before it ferments Fructose.

In wines like Port, the addition of neutral grape spirits stuns the yeast and halts fermentation, leaving a wine with a higher proportion of fructose sugars and creating a sweet wine.Fructose, along with glucose, is one of the principle sugars involved in the creation of wine. At time of harvest, there is usually an equal amount of glucose and fructose molecules in the grape; however, as the grape over ripens the level of fructose will become higher. In wine, fructose can taste nearly twice as sweet as glucose and is a key component in the creation of sweet dessert wines. During fermentation, glucose is consumed first by the yeast and converted into alcohol. A winemaker that chooses to halt fermentation (either by temperature control or the addition of brandy spirits in the process of fortification) will be left with a wine that is high in fructose and notable residual sugars. The technique of süssreserve, where unfermented grape must is added after the wine's fermentation is complete, this will result in a wine that tastes less sweet than a wine whose fermentation was halted. This is because the unfermented grape must will still have roughly equal parts of fructose and the less sweet tasting glucose. Similarly, the process of chaptalization where sucrose (which is one part glucose and one part fructose) is added will usually not increase the sweetness level of the wine. – Wiki - Sugars in Wine

ImplicationsSucrose is ideal for chaptalization of wines to be fermented dry.Two wines sweetened before bottling, one with Sucrose, one with Fructose (equal amounts) will have the same residual sugar (RS), but the Fructose sweetened wine will taste sweeter. (Note – after a few weeks, the acid in the wine will break down the Sucrose into its Glucose and Fructose components).During fermentation, the point where the Glucose and the Fructose starts being consumed may stress yeast, causing, among other things, a "stuck" fermentation.WRT sparkling wines, Sucrose is usually added for the second (bottle) fermentation and in the dosage to sweeten after disgorging. It may be more advantageous to use Glucose in the bottle fermentation, thus acclimating the yeast to it. Then, sweetening the dosage with Fructose, where what little yeast is left, would have difficulty fermenting it.

Thomas - "It is difficult to tell the difference between fully refined sugar produced from beet and cane." Both are sucrose. From: http://en.wikipedia.org/wiki/Sucrose.Tom - I'm not sure about laboratory grade. Fructose is a 5 carbon sugar ring; Glucose is a 6 carbon ring; Sucrose is a double sugar with a ring of each bonded together. On a scale that measures sweetness, Sucrose is assigned 100, Fructose calculates to 173 and Glucose 74 - http://en.wikipedia.org/wiki/FructoseTwo other links I read are:http://en.wikipedia.org/wiki/Glucosehttp://en.wikipedia.org/wiki/Sugars_in_wineOne of the interesting things, as I inferred above, is when we talk about RS in, say Riesling, we talk about acid balance, but all things being equal, the type of sugar(s) present in the finished wine could have just a great an impact.

Howie Hart wrote:One of the interesting things, as I inferred above, is when we talk about RS in, say Riesling, we talk about acid balance, but all things being equal, the type of sugar(s) present in the finished wine could have just a great an impact.

TomHill wrote:Which brings up the question: Is their any difference in taste between laboratory-grade Fructose & Glucose & Sucrose... other than just "sweet"???

Yes, there is. Consider the difference in taste between Coca-Cola bottled in the US vs. Coca-Cola bottled in Mexico. US Coke is sweetened with high-fructose corn syrup. Mexican Coke is sweetened with sucrose.

Howie, a side note about the “sweetness (perception) scale” based on 100- it represents the relative sweetness vs. a 10% sucrose/water solution (which is assigned 100). A 10% glucose/water solution is less sweet than a 10% sucrose/water solution and a 10% fructose/water solution is sweeter than a 10% sucrose/water solution. Put wine in the equation things become more complex.

If you look at the graph comparing various types of sugar in the Cornell article, fructose is sweeter but its “intensity” (“lasting power” or “aftertaste”) is shorter. According to Dr Yair Margalit (Concepts in Wine Chemistry) the recognition threshold for various types of sugars (sugar/water solutions) are listed as followsD-glucose is 16g/LD-fructose is 9 g/Lsucrose is 8 g/L

Victorwine wrote:...If you look at the graph comparing various types of sugar in the Cornell article, fructose is sweeter but its “intensity” (“lasting power” or “aftertaste”) is shorter. According to Dr Yair Margalit (Concepts in Wine Chemistry) the recognition threshold for various types of sugars (sugar/water solutions) are listed as followsD-glucose is 16g/LD-fructose is 9 g/Lsucrose is 8 g/L

Salute

It may be shorter, which would agree with my observation that wine sweetened with sucrose has a lingering, syrupy mouthfeel. After 1-2 months in the bottle, the sucrose breaks down and the finish is cleaner. Longer is not necessarily better.

As the acids in the wine slowly break down the sucrose (now having sucrose, glucose, fructose, and RS) does the wine appear “sweeter”? (Than the sucrose and RS only). According to the sweetness scale it should become sweeter. (Fructose is 1.73 times sweeter than glucose and inverted sugar is sweeter than sucrose) It’s because of the “intensity” of the sugars (and the make-up of the wine) that makes the wine seem “cleaner”. No? The fructose instead of bringing “sweetness” to the table might be enhancing ‘fruitiness” up front and the other sugars taming some of the “bite” and “sharpness” in the middle and back end.

He spoke at the Rochester conference a few years ago and was very good. One point he makes in the paper is the messiness caused bench trials by the time lapse of sugar break downs. My own bench trials are often uninformative, something that seems just right at the time is not so right tasted a month later, and that could well be the reason.

There seems to be a conflict in our sources, which I can't seems to resolve. From the Cornell article you referenced:

If sugar in the form of sucrose (table sugar) is back added, the sucrose will break down into 50% glucose and 50% fructose. This mixture, known as invert sugar, is sweeter than sucrose itself and is less sweet than pure fructose.

In the Fructose article I referenced above, http://en.wikipedia.org/wiki/Fructose, there is a graph that shows a sweetness scale, giving the following numbers:Fructose - 173Sucrose - 100Glucose - 73.4Invert Sugar - 50My experience is that the sweetness level of wine sweetened with sucrose does not seem to change over time, but the mouthfeel becomes cleaner.

My comment about bench trials was prompted by what Gerling says just after the section you quoted: "The enzymes and acids in wine will complete this conversion in roughly a year, which is one potential cause of perceived change during the first few months in bottle and also a consideration during bench trials for sweetening.

Hi Howie,This is how I use the "sweetness scale". Lets say I like what 10 g of sucrose delievered. To replace the sucrose with "pure" fructose (obtaining "similar" sweetness) I would only have to use 5.78 g of fructose (10 X 100 = 1000. 1000/173 = 5.78).If I wanted to replace the sucrose with "pure" glucose I would have to use 13.62 g of glucose (10 x 100 = 1000. 1000/73.4 = 13.62).

Yoikes....this chemistry stuff is way over the head of a simple little ole country computational physicist!! Does any of this discussion explain why sweet/dessert wines, like Sauternes, taste drier (dry out) as they geta lot of age on them?? Some sort of conversion from one sugar to another??Tom

TomHill wrote:Yoikes....this chemistry stuff is way over the head of a simple little ole country computational physicist!! Does any of this discussion explain why sweet/dessert wines, like Sauternes, taste drier (dry out) as they geta lot of age on them?? Some sort of conversion from one sugar to another??Tom

Tom, that's due to the (slow) esterification of the acids in the wine with the sugars. Once esterified, the sugars' perceived sweetness decreases substantially.

TomHill wrote:Yoikes....this chemistry stuff is way over the head of a simple little ole country computational physicist!! Does any of this discussion explain why sweet/dessert wines, like Sauternes, taste drier (dry out) as they geta lot of age on them?? Some sort of conversion from one sugar to another??Tom

Tom, that's due to the (slow) esterification of the acids in the wine with the sugars. Once esterified, the sugars' perceived sweetness decreases substantially.

Mark Lipton

I thought esterification took place between alcohol and another component like acid or sugar. Is that what you mean or am I misinformed?

Thomas wrote:I thought esterification took place between alcohol and another component like acid or sugar. Is that what you mean or am I misinformed?

Thomas, esters are formed between an acid (such as malic or tartaric or even acetic) and an alcohol. Because sugars are polyhydroxylated (i.e, lots of alcohols) they can react as alcohols. When there's enough around, they compete with ethanol in the esterification reactions.

Which is also why ethanol contributes a sweet taste to wine, because of those hydroxyls, one of the reasons that high alcohol wines always taste sweet and ripe, though it may be chemically dry. And also why paradoxically, high alcohol wines need greater acidity for balance than lower alcohol wines at the same degree of residual sugar..

Craig Winchell wrote:Which is also why ethanol contributes a sweet taste to wine, because of those hydroxyls, one of the reasons that high alcohol wines always taste sweet and ripe, though it may be chemically dry. And also why paradoxically, high alcohol wines need greater acidity for balance than lower alcohol wines at the same degree of residual sugar..

Yes, and also why I hypothesize that alcoholism and diabetes are related diseases.

Thomas wrote:I thought esterification took place between alcohol and another component like acid or sugar. Is that what you mean or am I misinformed?

Thomas, esters are formed between an acid (such as malic or tartaric or even acetic) and an alcohol. Because sugars are polyhydroxylated (i.e, lots of alcohols) they can react as alcohols. When there's enough around, they compete with ethanol in the esterification reactions.

Thomas wrote:I thought esterification took place between alcohol and another component like acid or sugar. Is that what you mean or am I misinformed?

Thomas, esters are formed between an acid (such as malic or tartaric or even acetic) and an alcohol. Because sugars are polyhydroxylated (i.e, lots of alcohols) they can react as alcohols. When there's enough around, they compete with ethanol in the esterification reactions.

I thought I'd update this, as I just finished bottling my 2013 Riesling. I started with about 150 lbs. of grapes, which yielded 12 gallons of juice at 18 Brix (% sugar). After a couple days of fermentation, when the Brix had dropped to 8, I drew off 2 gallons into 2-liter soda pop bottles and stored that in the freezer. I thawed this out on Wednesday and added it back to the wine before filtering and bottling. My reasoning, based on the above discussion, was to increase the fructose to glucose ratio in the RS of the final product. At this point, I'm quite pleased. The RS is about 1.6%, but has enough acid for balance. The finish is interesting. The sweetness is very clean, not cloying at all and at this point the wine reminds me of lemonade over rocks (real rocks). It reminds me of some Mosels I have had. I'm anxious to see how it is in a few months, after bottle-shock is over.

Hi Howie,Definitely sounds like a winner! How did you measure the RS? What was the TA at bottling? Your RS number pretty much coincides with the math. The 2 gals of Sussreserve, at 8 Brix (approximately 80 g/L of sugar) blended to 10 gals of wine (assuming fermented to dryness or completion) is like blending 1 part (sweet wine) to 5 parts (dry wine) thus diluting the sugar by 1/6 (1/6 X 80 = 13.3 g/L = 1.33% RS).What happens to the TA of the Sussreserve kept frozen for almost a year?

The TA dropped from .90 to .86 from juice to the final product. The Brix of the dry wine before blending was -1.0 and after blending was +0.6. I also have a spreadsheet file to calculate Pearson's Square that I used to figure out the sugar and alcohol. It gave me numbers of 1.6 for the RS and 9.5 for the ABV. I did not test the frozen juice, except for Brix, when I drew it off. Also, when I tasted it, it did not taste like it 2%. The difference in mouthfeel between this and regular sussreserve I've done in the past, or sweetening with table sugar is noticeable. I will be repeating this.